1. Field of the Invention
This invention pertains to automatic disc changers; particularly those of the type wherein multiple data discs are held in close proximity, in a common receptacle or tray, and transferred one at a time between the tray and a processing station (typically, a location where information is read from and/or written to the discs).
Discs of the type presently contemplated include those commonly known as compact discs (CD's), which are used to store digital information for computers (e.g. digital data and computer programs), and information representing reproducible audio and/or video presentations that do not require a computer for reproduction. Such compact discs may have differing recording formats and playback protocols, and different names indicating their usage; e.g. names such as CD-ROM (compact disc--read only memory), CDR (compact disc--recordable), etc. Their names, recording formats and playback protocols have no specific relevance to the present invention.
The present invention is concerned particularly with providing automatic disc changer apparatus, and an associated method of disc handling, that is safer and more efficient than known prior systems.
Terminology
Controlled drive: (also "controllably driven") connotes transfer of discs over a defined range, by edge drive, with bottom and top edges constrained in a manner allowing the rate of movement to be optimized throughout the range, without compromising disc safety. PA0 Disc Reader: a unit such as a CD-Rom drive, for performing a processing action on discs including actions such as reading and writing. PA0 Safe and efficient: connotes efficient handling of discs without compromising the integrity of storage; "efficient" connoting quick and cost-effective handling of large numbers of discs (e.g. 400 discs in a disclosed preferred embodiment). PA0 Station: position or place containing a disc reader and a platform from which discs are moved to the reader and to which discs are moved from the reader. PA0 Idle Station: a station not holding a disc, and not in the process of loading or unloading a disc (see Loading and Unloading below). PA0 Transfer: connotes movement of a disc between a tray and a station. PA0 Loading: transfer of a disc from a tray to a station. PA0 Unloading: transfer of a disc from a station to a tray.
2. Prior Art
Presently known automatic disc changer systems are rather expensive and slow acting. For example, one known system has an average access time (the time for locating a disc and transferring it to a station) on the order of 15 seconds. Such systems also are constrained by safety considerations to handle fewer discs than would be desired in many applications.